This invention relates to the field of dental composite resin restorations. Composite dental restorative materials are described in U.S. Pat. No. 3,066,112, issued in November 1962. Current practice in filling cavities with cosmetically appealing compositions involves the use of resins mixed relatively homogeneously with a very finely divided or colloidal filler. There are a number of undesirable characteristics of present composite materials and restorations made from them. Some of these include the problem of polymerization shrinkage, high coefficient of thermal expansion relative to the tooth crown, and low stiffness (modulus of elasticity). The shrinkage tends to allow contraction gaps and microleakage around the restorations. The differential coefficient of thermal expansion tends to promote the microleakage and staining of the margins of the restoration. The low stiffness of the restoration results in loss of support of remaining tooth structures.
Composite resin dental materials of this type are, for example, described in U.S. Pat. No. 4,215,033, issued July 29, 1980, and in Bowen et al., "Semiporous Reinforcing Fillers For Composite Resins: I. Preparation of Provisional Glass Formulations," 55 J. Dent. Res. 738-47 (1976), and Bowen et al., "Semiporous Reinforcing Fillers For Composite Resins: II. Heat Treatments and Etching Characteristics," 55 J. Dent. Res. 748-56 (1976). See also, Bowen et al., "Theory of Polymer Composites," International Symposium on Posterior Composite Resin Dental Restorative Materials, 95-107 (Peter Szulc Pub., The Netherlands, 1985), and references cited in each of the above articles and patent.
U.S. Pat. No. 4,215,033 in particular describes a transparent glass filler material in which the glass is separated into two interconnected vitreous phases which after crushing and ball milling to a very fine powder, is acid etched to produce a porous surface layer. Preferred glass compositions disclosed in this patent include a mixture of silicon dioxide, boron oxide, aluminum oxide and strontium oxide, with one or more from the group of calcium oxide, zinc oxide, stannic oxide, and ziroconium oxide as optional modifying ingredients. The transparent inorganic glass particles of microscopic size are silane treated and then combined with an organic resin to provide an improved composite dental material.